Display apparatus and electronic equipment

ABSTRACT

A display apparatus has a compressor cooler having a condenser that condenses refrigerant by radiating heat, an evaporator that evaporates the refrigerant for heat absorption and dehumidification, and a compressor that inhales vapor generated by the evaporator and compresses the vapor to be condensed; a temperature sensor that monitors temperature of the evaporator; a backlight; a first control portion that terminates the compressor when the temperature of the evaporator is a first predetermined temperature or lower; and a second control portion that increases a level of the backlight when the temperature of the evaporator is a second predetermined temperature or lower, wherein the second predetermined temperature is higher than the first predetermined temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2010-265512 filed on Nov. 29, 2010, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display apparatus and electronic equipment.

2. Description of Related Art

Recent years, a liquid crystal display apparatus is used for digital signage. Such display apparatus has a sealed structure, because the apparatus may be installed outdoors and thus it is necessary to prevent water or dust from entering into the apparatus. In addition, these display apparatus can display with high luminance in order to keep the visibility in the outdoors.

When the display apparatus is displaying an image with high luminance, or when it is being irradiated by sunlight, heat is generated inside the housing of the apparatus. As for the display apparatus having a sealed structure as described above, it is difficult for the heat generated inside the housing to dissipate outside the housing. As a result, temperature inside the housing may rise and a malfunction of liquid crystal in the liquid crystal display apparatus may occur.

One improvement is to employ a compressor-based cooling system into those LCD displays in order to solve the above-mentioned problems as described in JP 2010-164884A1 which was filed by the applicant. The disclosures of which are hereby incorporated by reference as if set forth in full herein.

However, in the above-mentioned liquid crystal display apparatus, since the display apparatus is sealed structured, a dew-condensation in the housing may occur. In particular, during a cold winter season, since the outside temperature becomes lower than the temperature inside the housing, the temperature difference between the outside and the inside of the housing may cause a dew-condensation on a protection glass arranged in the front side of the liquid crystal panel. This dew-condensation decreases visibility of an image displayed on the liquid crystal panel. In order to avoid this dew-condensation, one idea is to perform dehumidification by activating a cooler when a humidity level becomes a certain level or higher. However, if the cooler is activated when the ambient temperature is low, its evaporation temperature decreases and the refrigerant pressure inside the evaporator becomes too low. This may cause a safety problem for cooler.

SUMMARY OF THE INVENTION

A display apparatus according to the present invention includes a compressor refrigerator including a condenser that condenses refrigerant by thermal radiation, an evaporator that evaporates the refrigerant so as to perform heat absorption and dehumidification, and a compressor that inhales vapor generated by the evaporator and increases the pressure of the vapor to be condensed, a temperature sensor that monitors temperature of the evaporator, a backlight, a first control portion that stops the compressor when the temperature of the evaporator is a first predetermined temperature or lower; and a second control portion that increases a level of the backlight when the temperature of the evaporator is lower than or equal to a second predetermined temperature that is higher than the first predetermined temperature.

In addition, electronic equipment according to the present invention includes a cooler including at least a compressor, a temperature sensor that measures temperature, a humidity sensor that measures humidity, and a control portion that activates the compressor when the temperature measured by the temperature sensor is higher than a first temperature and stops the compressor when the measured temperature is lower than a second temperature that is lower than the first temperature, wherein the control portion also activates the compressor when the measured temperature is between the first temperature and the second temperature, and the humidity measured by the humidity sensor is higher than a predetermined humidity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a structure of a display apparatus 1.

FIG. 2 is a first cross sectional view illustrating the structure of the display apparatus 1.

FIG. 3 is a second cross sectional view illustrating the structure of the display apparatus 1.

FIG. 4 is a diagram illustrating a structure of cooler 30.

FIG. 5 is a block diagram of the display apparatus 1.

FIG. 6 is a flowchart illustrating a first example of temperature and humidity control performed by the display apparatus 1.

FIG. 7 is a flowchart illustrating a second example of temperature and humidity control performed by the display apparatus 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of a display apparatus according to the present invention will be described with reference to the attached drawings. First, a structure of the display apparatus will be described with reference to FIGS. 1 to 3.

<Structure of Display Apparatus>

FIG. 1 is a perspective view illustrating a structure of a display apparatus 1. The display apparatus 1 has an upper housing 10 which is the housing on the upper part side and a lower housing 20 which is the housing on the lower part side. The upper housing 10 has a window part 11 so that an image displayed on a liquid crystal panel 12 (described later) arranged inside the upper housing 10 is viewable. The window part 11 is made of material which is transparent against a visible light such as glass.

FIG. 2 is a diagram illustrating an A-A cross sectional view of the display apparatus 1 illustrated in FIG. 1.

As illustrated in FIG. 2, inside the upper housing 10, the liquid crystal panel 12 displaying an image, a backlight 13 irradiating light to the panel 12, fans 14 a and 14 b circulating air inside the upper housing 10, temperature sensors 15 a and 15 b detecting temperature inside the upper housing 10 (see FIG. 3 for detail), humidity sensors 17 a and 17 b detecting humidity inside the upper housing 10, and an evaporator 31 cooling the inside of the upper housing 10 so as to perform dehumidification are arranged.

Further, as illustrated in FIG. 2, inside the lower housing 20, a compressor 32 compressing refrigerant, a condenser 33 condensing the refrigerant compressed by the compressor 32 by heat radiation, and an expansion valve 34 that expands the refrigerant condensed by the condenser 33 are arranged. The evaporator 31 absorbs heat by evaporating the refrigerant expanded by the expansion valve 34. The compressor 32 compresses the refrigerant evaporated by the evaporator 31. Hereafter, group that consist of the evaporator 31, the compressor 32, the condenser 33, and the expansion valve 34 is referred to as a cooler 30. Details of this cooler 30 will be described later.

The liquid crystal panel 12 controls orientation of liquid crystal so as to selectively transmit light from the backlight 13, and hence an image is displayed. The image displayed on the liquid crystal panel 12 is viewable from the outside of the upper housing 10 through the window part 11. The backlight 13 is constituted of, for example, a fluorescent tube or light emitting diodes. The backlight 13 may comprise a diffuser panel that diffuses light emitted from the light source so as to irradiate a plane (or uniform) light to the liquid crystal panel 12, and a reflector plate that reflects light emitted from the light source.

The fan 14 b is arranged at a lower portion of the upper housing 10 and blows cooled air cooled by the evaporator 31 towards a front surface of the liquid crystal panel 12. The fan 14 a is arranged at an upper portion of the upper housing 10 and blows air which has passed the front surface side of the liquid crystal panel 12 to the rear side of the panel 12. Then, this air further passes the rear side of the liquid crystal panel 12 and reaches the evaporator 31. By circulating the air inside the upper housing 10 using the fans 14 b and 14 a, the liquid crystal panel 12 is cooled effectively. The number or arrangement of the fans 14 b and 14 a are not limited to the above example. Hereafter, the fans 14 b and 14 a are generically referred to as a fan 14.

FIG. 3 is a diagram illustrating a B-B cross sectional view of the display apparatus 1.

As illustrated in FIG. 3, four temperature sensors 15 a, 15 b, 15 c, and 15 d are arranged inside the upper housing 10. Further, four humidity sensors 17 a, 17 b, 17 c, and 17 d are also arranged inside the upper housing 10. Each of the temperature sensors 15 a, 15 b, 15 c, and 15 d is constituted of a temperature detecting element such as a thermistor for example. Each of the humidity sensors 17 a, 17 b, 17 c, and 17 d is constituted of a humidity detecting element such as a high polymer humidity sensing element, which is an element that detects humidity based on a variation of an electrical characteristic (such as resistance or capacitance) of high polymer according to moisture). As illustrated in FIG. 2, each of the above-mentioned temperature sensors 15 a to 15 d and the humidity sensors 17 a to 17 d are disposed between the window part 11 and the liquid crystal panel 12.

The temperature sensor 15 a and the humidity sensor 17 a are arranged on the upper right side of the window part 11. The temperature sensor 15 b and the humidity sensor 17 b are arranged on the lower right of the window part 11. The temperature sensor 15 c and the humidity sensor 17 c are arranged on the upper left side of the window part 11. The temperature sensor 15 d and the humidity sensor 17 d are arranged on the lower left side of the window part 11. However, the arrangement of the temperature sensors or the humidity sensor is not limited to the above. For instance, only a single humidity sensor may be arranged near the evaporator 31.

<Schematic Structure of Cooler>

With reference to FIG. 4, a structure of the cooler 30 will be described.

The cooler 30 includes an evaporator 31, the compressor 32, the condenser 33, and the expansion valve 34. In this cooler 30, the refrigerant circulates in a closed loop, and there is no need to exchange the refrigerant.

The compressor 32 compresses the refrigerant evaporated by the evaporator 31 so that the refrigerant becomes a high temperature and high pressure state. The condenser 33 condenses the refrigerant compressed by the compressor 32, by heat exchange (heat radiation). The cooler 30 may include a fan for expediting the heat exchange in the condenser 33.

The expansion valve 34 expands the refrigerant condensed by the condenser 33 so that the refrigerant becomes a low temperature and low pressure state. Then, the evaporator 31 evaporates the refrigerant expanded by the expansion valve 34 by heat exchange (heat absorption). Here, moisture contained in the air inside the upper housing 10 is dew-condensed on the evaporator 31. Then, moisture dew-condensed on the evaporator 31 is drained outside the upper housing 10. The cooler 30 may include a fan for expediting heat exchange or dehumidification in the evaporator 31.

As described above, the cooler 30 cools and dehumidify the inside of the upper housing 10, by changing the state of the refrigerant between liquid and gas repeatedly and by the exchanging heat (heat absorption and radiation).

At inlet of the evaporator 31 in a flow path of the refrigerant, evaporator temperature sensor 311 detecting temperature of the evaporator 31 or evaporator pressure sensor 312 detecting pressure of the evaporator 31 is arranged. Further, at outlet of the condenser 33, a condenser temperature sensor 332 detecting temperature of the condenser 33 and a condenser pressure sensor 331 detecting pressure of the condenser 33 are arranged.

Each of the evaporator temperature sensor 311 and the condenser temperature sensor 332 has a temperature detecting element (e.g., a thermistor). The evaporator temperature sensor 311 indirectly detects temperature of the refrigerant flowing into the evaporator 31. In detail, the sensor 311 detects temperature of the refrigerant between outgoing from expansion valve 34 and ingoing to evaporator 31. The condenser temperature sensor 332 detects temperature of the refrigerant flowing out from the condenser 33. In detail, the sensor 332 indirectly detects temperature of the refrigerant condensed by the condenser 33 before it is expanded by the expansion valve 34.

In the cooler 30, if the flow path of the refrigerant is in a “closed loop”, a relationship between the pressure and the temperature of the refrigerant is uniquely determined. Therefore, by referring to the temperature detected by the evaporator temperature sensor 311, the pressure of the refrigerant can be estimated.

Instead, the pressure of the refrigerant may be measured directly using pressure sensors 312 and 331 may be adopted. These pressure sensors have a pressure detecting element such as a strain gage (which detects deformation of diaphragm caused by pressure of the refrigerant).

<Control of Temperature and Humidity>

The control of temperature and humidity of the display apparatus 1 is described with reference from FIGS. 5 to 7. FIG. 5 is a block diagram illustrating a schematic structure of the apparatus 1.

As illustrated in FIG. 5, the display apparatus 1 has a control portion 16 that controls operations of the cooler 30, the liquid crystal panel 12, the backlight 13, and the fan 14. The control portion 16 obtains information detected by the temperature sensor 15, the humidity sensor 17, the evaporator temperature sensor 311, and the condenser temperature sensor 332.

The cooler 30 is designed to terminate its operation when the pressure of the evaporator 31 becomes lower than a predetermined pressure. The cooler 30 is designed to terminate because when the refrigerant pressure inside the evaporator is too low, it may make cooler 31 harmful. A decrease of the refrigerant pressure is equivalent to a decrease of the refrigerant temperature inside the evaporator. In addition, the cooler 30 is specified to stop at the safety point of view when the pressure of the condenser 33 detected by the condenser pressure sensor 331 becomes Pc 1 or higher.

[First Example of Temperature and Humidity Control]

FIG. 6 is a flowchart showing an example of temperature and humidity control performed by the display apparatus 1. This flowchart shows the control performed recursively by the control portion 16. This flowchart can be roughly divided into a process of Steps S1 to S6 and a process of Steps S7 to S11. The former one is for preventing a malfunction due to an increase of temperature in the housing, and the latter is a process for preventing a malfunction due to a decrease of temperature in the housing.

First, the former process is discussed. As shown in FIG. 6, first, in Step S1, the control portion 16 detects the temperature inside the upper housing 10, referring to outputs of the temperature sensors 15.

In Step S2, the control portion 16 determines whether the temperature detected in Step S1 is temperature Th-or-higher or not. For instance, it determines whether at least one of the sensors 15 a to 15 d measures the temperature Th or higher. Here, Th is a temperature that is lower than an upper limit temperature that normal display on the liquid crystal panel 12 is guaranteed. For example, the temperature is 43 degrees centigrade.

If the temperature inside the housing 10 is Th or higher (Yes in Step S2), the control portion 16 proceeds to Step S3 and drives the cooler 30. Here, if the cooler 30 is already being driven, this driving state is maintained. In this case, the control portion 16 may drive the fan 14 together with the driving of the cooler 30.

On the other hand, if the temperature inside the housing 10 is lower than Th (No in Step S2), the control portion 16 proceeds to Step S4 and detects humidity inside the housing 10.

In Step S5, the control portion 16 determines whether the humidity inside the housing 10 is Hh-or-higher or not. For instance, it determines whether at least in one of the sensors 17 a to 17 d measures a humidity Hh-or-higher or not(Hh is for example, 80%).

If the humidity inside the housing 10 is Hh or higher (Yes in S5), assuming that the dew-condensation may occur, the control portion 16 proceeds to Step S3 and drive the cooler 30. Thus, the dew-condensation can be prevented. If the humidity inside the housing 10 is lower than Hh (No in S5), the driving of the cooler 30 is stopped in Step S6. Because the temperature inside the upper housing 10 is in a normal range and there is no risk of the condensation, the control portion 16 stops the driving of the fan 14 in synchronization with the cooler 30.

Next, the latter process is discussed. First, in Step S7, the control portion 16 detects temperature of the evaporator 31 referring to an output of the evaporator temperature sensor 311.

In Step S8, the control portion 16 determines whether the temperature detected in Step S7 is Te2-or-lower or not. Here, Te2 is a temperature a little higher than a lower limit temperature that normal operation of the evaporator 31 is guaranteed. This temperature is referred to as temperature Te1.

When the temperature of the evaporator 31 is Te2 or lower (Yes in Step S8), the control portion 16 controls an output level of the backlight 13 to be a level higher than a normal level so as to prevent the temperature from decreasing down to the temperature Te1.

For instance, if the guaranteed temperature Te1 is −15 degrees centigrade, the control portion 16 controls the level of the backlight 13 to be 65% of the maximum value when the temperature of the evaporator 31 lowers −10 degrees. If the temperature lowers −12 degrees, the level of the backlight 13 is controlled to be 80%. By making the output level of the backlight high, inside the display apparatus 1 is heated and the temperature of the refrigerant rises. As a result, a decrease of the evaporation temperature (evaporate pressure) is prevented, and hence it can prevent the cooler from terminating unintentionally. Further, since the cooler is prevented from termination, dew-condensation at a low temperature can be avoided.

When the temperature of the evaporator 31 is Te1 or lower (Yes in Step S10), the cooler 30 is terminated in Step S11.

In this case, the control portion 16 may also terminate the operation of the liquid crystal panel 12 and the backlight 13.

According to this example, it is possible to prevent dew-condensation, while safety of the cooler 30 is maintained.

[Second Example of Temperature and Humidity Control]

FIG. 7 is a flowchart showing another example of the temperature and humidity control performed by the display apparatus 1. In the first example described above, the level of the backlight is controlled based on the detection result of the temperature of the evaporator. However, this example differs that the level of the backlight is controlled based on the humidity inside the upper housing 10 rather than based on the detection result of the temperature of the evaporator.

As shown in FIG. 7, first, in Step S21, the control portion 16 detects the temperature inside the upper housing 10. In Step S22, the control portion 16 determines whether the temperature detected in S21 is Th-or-higher or not. If the temperature is lower than Th (NO in S22), the humidity inside the upper housing 10 is detected (S23). If the humidity is lower than Hh (NO in S24), the cooler 30 is terminated (S25).

On the other hand, if the temperature inside the upper housing 10 is Th or higher (YES in S22), the control portion 16 drives the cooler 30 (S26).

If the temperature inside the upper housing 10 is lower than Th (NO in S22) and the humidity is Hh or higher (YES in S24), the cooler 30 is driven (S27). Further, the backlight 13 is controlled so as to increase its output level (S28). As described above, the level of the backlight is increased when the cooler 30 (compressor) is driven based on the humidity in the housing. Thereby, it can increase the heat load even when the temperature inside the housing is low.

In this case, the control portion 16 adjusts the level of the backlight 13 to a predetermined level (80%, for example) regardless of the temperature of the evaporator 31. If the level of the backlight 13 is already larger than predetermined value, the control portion 16 may maintain the level of the backlight 13.

<Variations>

In order to prevent the cooler 30 from frequent activation and termination, the control portion 16 may additionally perform following control in the flowchart shown in FIG. 6 or 7. For example, in Step S2 of FIG. 6 and Step S22 of FIG. 7, the threshold value temperature Th may be set different value depending on whether the cooler 30 is to be activated or to be terminated. For example, 43 degrees centigrade may be adopted when driving, and 38 degrees centigrade when terminating. In other words, the threshold value temperature Th may have a hysteresis. The control portion 16 may perform a control so as not to terminate the cooler 30 while a predetermined time period (for example, ten minutes) has not elapsed since the activation of the cooler 30. The vice-versa control may be performed (i.e. do not activate while a predetermined time has not elapsed since the termination)

Instead of steps S7 to S10 shown in FIG. 6, in which the backlight or the cooler 30 are controlled according to the temperature of the evaporator 31, these controls may be performed according to temperature of the condenser 33. However, it is preferable, to perform control based on temperature of the condenser 33 after a predetermined time period (for example, 10 minutes) has elapsed from the activation of the cooler 30 so that the temperature of the condenser 33 is raised and stabilized.

The embodiment of the present invention is described above, however, the scope of the present invention is not limited to this. It can be modified variously within the scope of the present invention without deviating from the spirit thereof. 

1. A display apparatus comprising: a compressor cooler having a condenser that condenses refrigerant by radiating heat, an evaporator that evaporates the refrigerant for heat absorption and dehumidification, and a compressor that inhales vapor generated by the evaporator and compresses the vapor to be condensed; a temperature sensor that monitors temperature of the evaporator; a backlight; a first control portion that terminates the compressor when the temperature of the evaporator is a first predetermined temperature or lower; and a second control portion that increases a level of the backlight when the temperature of the evaporator is a second predetermined temperature or lower, wherein the second predetermined temperature is higher than the first predetermined temperature.
 2. The display apparatus according to claim 1, further comprising: a humidity sensor that measures humidity; and a third control portion that activates the compressor cooler at a predetermined humidity or higher, and further increases a level of the backlight when the evaporator becomes a second predetermined temperature or lower.
 3. An electronic device comprising: a cooler having at least a compressor; a temperature sensor that measures temperature; a humidity sensor that measures humidity; and a control portion that activates the compressor when the temperature measured by the temperature sensor is higher than a first temperature and terminates the compressor when the measured temperature is lower than a second temperature that is lower than the first temperature, wherein the control portion also activates the compressor when the measured temperature is between the first temperature and the second temperature, and the humidity measured by the humidity sensor is higher than a predetermined humidity. 